It is very important that materials used for artificial organs in general should not cause any toxic, carcinogenic, pyrogenic or allergic effect nor any adverse tissue or skin reaction, etc. in the body.
In particular, materials of vascular grafts which are used to replace surgically damaged blood vessels should have flexibility as well as anti-thrombogenic properties and be easy to fabricate.
Nylon, polyester, polytetrafluoro ethylene (PTFE), polypropylene, polyacrylonitrile, etc. have been used as materials to fabricate vascular grafts. Among them PTFE and polyester are now widely used since they do not have significant property changes in the body after long term use. Polyester, in particular polyethylene-terephthalate (trade name: Dacron), is most widely used as the material of vascular grafts because it is easy to handle and easy to fabricate.
In case the said polymer materials are used, the fabrication state or porosity of the materials has great significance. The porosity of vascular grafts plays an important role for their long-term patency and overall biological performance. The porosity of the vascular grafts allows easy handling and anastomosis, and good flexibility. It also facilitates transmural ingrowth of connective tissue into the grafts and better healing into the surrounding tissue. Therefore, the porosity is an essential component for long term function of vascular grafts. The main disadvantage of highly porous vascular grafts is their high permeability for blood during implantation. It may result in severe blood leakage through the graft wall. Thus, the grafts must be preclotted with blood before the implantation to obtain zero permeability. Generally the grafts are immersed in or flushed with fresh blood of patient to preclot the wall surface. But the preclotting process is often time-consuming, causes blood transfusion, and may lead to increased usage of the patient's blood. In the case of an emergent patient with large bleeding by an accident, it may be fatal. It is also dangerous when the patient has been systematically heparinized for surgery.
Many research works have been done to develop new vascular grafts, which are blood tight during implantation and thus eliminate the need for preclotting the grafts, and become sufficiently porous to facilitate tissue ingrowth and biological healing. Most commonly used methods include coating or impregnation of the porous graft with a biodegradable component. The coated or impregnated vascular graft is blood tight during the implantation. Due to its gradual degradation and dissolution in the body, the resorbable material creates increasingly large pores in the initially impervious graft, allowing the ingrowth of periprosthetic tissue.
Until now, various proteins have been used as the biodegradable components for coating or impregnation of the grafts. They include albumin, gelatin or elastin, collagen, and fibrin. The vascular grafts pre-treated with these proteins showed little blood loss and faster healing compared to the grafts preclotted with blood.
However, in the case the vascular grafts are impregnated with above proteins, there is a problem that the proteins are easily denatured when the grafts are manufactured. The proteins are also not easy to make compatible with usual storage and sterilization procedures.
Thus, the objective of the present invention is to develop an improved vascular graft fabricated of a polyester fiber which is impregnated with non-proteinaceous materials, polysaccharides or their derivatives, which are biodegradable and biocompatible. The said vascular graft is blood tight during the implantation and persists its high porosity for tissue ingrowth and biological healing.
Consequently, the purpose of the present invention consists in providing an improved artificial blood vessel fabricated of a polyester fiber which is surface-treated and then impregnated with polysaccharides or their derivatives.